(a) Field
The present invention relates to a fuel cell stack. More particularly, the present invention relates to an end plate for a fuel cell stack.
(b) Description of Related Art
A fuel cell system includes a fuel cell stack that generates electrical energy using the electrochemical reaction between a fuel (hydrocarbon-based fuel, pure hydrogen, or reformed gas rich in hydrogen) and an oxidizing agent (air or pure oxygen). A direct oxidation type fuel cell uses a liquid or gas hydrocarbon-based fuel, and a polymer electrolyte type fuel cell uses pure hydrogen or a reformed gas rich in hydrogen.
The fuel cell stack includes membrane-electrode assemblies (MEAs), separators positioned between the membrane-electrode assemblies and supplying a fuel and an oxidizing agent to the membrane-electrode assemblies, and a pair of end plates positioned outside the outermost separator and pressing the membrane-electrode assemblies and the separators together to fix them as one body.
The end plate generally includes a fuel inlet, an oxidizing agent inlet, a fuel outlet, and an oxidizing agent outlet. The fuel introduced into the fuel inlet is provided to the anode of the membrane-electrode assemblies while passing through a fuel channel of the separator, and non-reacted fuel is discharged through the fuel outlet. The oxidizing agent introduced into the oxidizing agent inlet is provided to the cathode of the membrane-electrode assemblies while passing through an oxidizing agent channel of the separator, and the non-reacted oxidizing agent is discharged through the oxidizing agent outlet.
The oxidizing agent is humidified to a predetermined humidity by using a humidifying device before the introduction of the oxidizing agent to the fuel cell stack, or external air may be introduced as is, without humidifying. However, when using the humidifying device, the volume of the fuel battery system is increased, manufacturing costs are increased, and a water supply source and a pump for supplying the water to the humidifying device are required. Meanwhile, when air that is not humidified is introduced as is, the region that is initially supplied with the oxidizing agent becomes very dry with respect to the cathodes of the membrane-electrode assemblies, such that the membrane-electrode assemblies may be deteriorated.
That is, moisture is generated as a byproduct of the electrochemical reaction inside the fuel cell stack, however the electrochemical reaction is not active in the region that is initially supplied with the oxidizing agent with respect to the cathodes, such that a dry state is maintained. The dry state can cause radicals generated during the operation of the membrane-electrode assembly to be sustained in the membrane-electrode assembly for a long time, such that deterioration of the membrane-electrode assembly may be accelerated.
The above information disclosed in the Background section is only for enhancement of understanding of the background of the invention, and therefore may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.